On Fri, Feb 23, 2024 at 6:34 PM Ask Bjørn Hansen <a...@develooper.com> wrote: > The relay server `dhcplb` could, maybe, help in that scenario > (dhcplb runs on the anycast IP, the “real” DHCP servers on > unicast IPs behind dhcplb).
Although they used the word "anycast", they're just load balancing. Devices behind a load balancer are not "anycast," since the load balancer explicitly decides which machine gets which transaction. Even with clever load balancers like Linux Virtual Server in "routing" mode where the back-end servers all share the virtual IP address, that's load balancing, not anycast routing. An IP is not "anycast" unless it moves via anycast routing. Anycast routing means it's announced into the _routing protocol_ from multiple sources on behalf of multiple distinct machines. In their readme, they comment that their load balancer replaced attempts to use anycast routing with equal cost multipath. That makes good sense. Relying on ECMP for anycasted DHCP would be a disaster during any sort of failure. Add or remove a single route from an ECMP set and the hashed path selection changes for most of the connections. All the DHCP renewals would very suddenly be going to the wrong DHCP server. Where anycast works, it works because ECMP only rarely comes into play. Regards, Bill Herrin -- William Herrin b...@herrin.us https://bill.herrin.us/
